Greg: Regression Helper Functions

Methods for manipulating regression models and for describing these in a style adapted for medical journals.
Contains functions for generating an HTML table with crude and adjusted estimates, plotting hazard ratio, plotting model
estimates and confidence intervals using forest plots, extending this to comparing multiple models in a single forest plots.
In addition to the descriptives methods, there are addons for the robust covariance matrix provided by the sandwich
package, a function for adding non-linearities to a model, and a wrapper around the Epi package's Lexis functions for
time-spliting a dataset when modeling non-proportional hazards in Cox regressions.